read-tree -u one-way merge fix to check out locally modified paths.

The "-u" flag means "update the working tree files", but to
other types of merges, it also implies "I want to keep my local
changes" -- because they prevent local changes from getting lost
by using verify_uptodate.  The one-way merge is different from
other merges in that its purpose is opposite of doing something
else while keeping unrelated local changes.  The point of
one-way merge is to nuke local changes.  So while it feels
somewhat wrong that this actively loses local changes, it is the
right thing to do.

Signed-off-by: Junio C Hamano <junkio@cox.net>

read-tree.c

@@ -686,6 +686,9 @@ static int oneway_merge(struct cache_entry **src)
 	if (!a)
 		return deleted_entry(old, NULL);
 	if (old && same(old, a)) {
+		struct stat st;
+		if (lstat(old->name, &st) || ce_match_stat(old, &st, 1))
+			old->ce_flags |= htons(CE_UPDATE);
 		return keep_entry(old);
 	}
 	return merged_entry(a, NULL);